Circuit of Reducing Power Loss of Switching Device

ABSTRACT

A circuit is provided to reduce power loss on switching. A pair of auxiliary switching devices is switched on before a pair of switching devices. The switching devices are switched on after a corresponding capacitor to the auxiliary switching devices is discharged to zero. Thus, the power loss of the switching devices is reduced.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This application claims priority from Taiwan Patent Application No.098130509, filed in the Taiwan Patent Office on Sep. 10, 2009, entitled“Circuit of Reducing Power Loss of Switching Device” and incorporatesthe Taiwan patent application in its entirety by reference.

TECHNICAL FIELD

The present disclosure relates to reducing power loss; moreparticularly, relates to drive a load by a switching inverter connectedwith a high-voltage direct-current (DC) bus while power loss happenedbetween turning on and off metal-oxide semiconductor field-effecttransistor (MOSFET) is reduced.

DESCRIPTION OF THE RELATED ARTS

Generally, a power system having a low voltage and a big current raisesits voltage level to reduce current for decreasing power loss, while thepower system having the raised voltage output power through a switchinginverter composed of switches. Although the power loss is thus reduced,the switches still have switching loss and efficiency of the wholesystem is not well improved.

In FIG. 6, a general switching inverter 4 comprises two pairs ofswitching devices 5, 6 and an alternative-current (AC) inductor 7, wherethe switching devices 5, 6 and the AC inductor 7 are serially connected.Therein, the first switching device 5 comprises a first switch 51 and asecond switch 52; the second switching device 6 comprises a third switch53 and a fourth switch 54; the first switch 51 and the second switch 52are serially connected with each other; and, the third switch 53 and thefourth switch 54 are serially connected with each other. Thedisadvantage of such a switching inverter is a high switching loss onturning on and off transistor. When a drain-source voltage (Vs.) of anyswitching device 5,6 is not reduced to zero, a current is generated toflow through the switching device 5,6 so that a switching loss ishappened to the switching device 5,6. As a result, quality of the deviceis affected, electronic utilities around are interfered, and powersource becomes not reliable. Hence, the prior arts do not fulfill allusers' requests on actual use.

SUMMARY OF THE DISCLOSURE

The main purpose of the present disclosure is to drive a load by aswitching inverter connected with a high voltage DC bus while power losshappened between turning on and off MOSFET is reduced.

To achieve the above purpose, the present disclosure is a circuit ofreducing power loss of a switching device, comprising a pair ofauxiliary switching devices, a pair of diodes, a pair of switchingdevices, a pair of auxiliary inductors and a load circuit, where top legauxiliary switches and bottom leg auxiliary switches of the auxiliaryswitching devices are turned on earlier than top leg switches and bottomleg switches of the switching devices after a drain-source voltage of aparallel capacitor of a corresponding MOSFET is totally discharged.Accordingly, a novel circuit of reducing power loss of a switchingdevice is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be better understood from the followingdetailed description of the preferred embodiment according to thepresent disclosure, taken in conjunction with the accompanying drawings,in which

FIG. 1 is the view showing the preferred embodiment according to thepresent disclosure;

FIG. 2 is the view showing the switching loss;

FIG. 3A to FIG. 3F are the views showing the time series control modesof the circuit;

FIG. 4 is the view showing the state of use;

FIG. 5 is the view showing the time series control; and

FIG. 6 is the view of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description of the preferred embodiment is provided tounderstand the features and the structures of the present disclosure.

Please refer to FIG. 1 and FIG. 2, which are a view showing a preferredembodiment according to the present disclosure and a view showingswitching loss. As shown in the figures, the present disclosure is acircuit of reducing power loss of a switching device, comprising a pairof auxiliary switching devices 11, a pair of diodes 12, a pair ofswitching devices 13, a pair of auxiliary inductors 14 and a loadcircuit 15, where a switching inverter 1 connected with a high-voltagedirect-current (DC) bus is thus constructed to drive a load.

The pair of auxiliary switching devices 11, comprising a top legauxiliary switch 111 and a bottom leg auxiliary switch 112, is connectedwith a direct-current voltage 10, where the top leg auxiliary switch 111and the bottom leg auxiliary switch 112 are serially connected with eachother; and each of the top leg auxiliary switch 111 and the bottom legauxiliary switch 112 is an auxiliary metal-oxide semiconductorfield-effect transistor (MOSFET).

The pair of diodes 12, comprising a first diode 121 and a second diode122, is connected with the pair of auxiliary switching devices 11.

The pair of switching devices 13 comprises a top leg switch 131 and abottom leg switch 132, where the top leg switch 131 and the bottom legswitch 132 are serially connected with each other; each of the top legswitch 131 and the bottom leg switch 132 is a switching MOSFET; and eachof the top leg switch 131 and the bottom leg switch 132 is parallellyconnected with a resonant capacitor 133,134.

The pair of auxiliary inductors 14 is connected with the pair ofauxiliary switching devices 11 and the pair of switching devices 13. Anauxiliary switching circuit 16 is constructed with the pair of auxiliaryinductors 14, the pair of auxiliary switching devices 11 and the pair ofdiodes 12 to fix each turn-on time of the top leg auxiliary switch 111and the bottom leg auxiliary switch 112. Therein, the pair of auxiliaryinductors 14 comprises a first inductor and a second inductor; the firstinductor and the second inductor are parallelly connected with eachother; each of the first inductor and the second inductor has a firstterminal and a second terminal; and, the second terminal of the secondinductor is connected with the second terminal of the first inductor.

The load circuit 15, comprising a load inductor 151 and a plurality ofload capacitors 152, is connected with the pair of switching devices 13.

On constructing the present disclosure, an auxiliary transformer isconstructed with the first inductor and the second inductor of theauxiliary inductor 14; a ratio of a coil number of a secondary side ofthe auxiliary transformer to a coil number of a primary side of theauxiliary transformer is 1:n; the first diode 121 and the second diode122 are connected with each other at a point through a terminal of thefirst diode 121 and a terminal of the second diode 122; the first diode121 and the second diode 122 are connected with the first terminal ofthe first inductor; the first terminal of the second inductor isconnected with a common terminal of the pair of auxiliary switchingdevices 11; the second terminal of the second inductor is connected witha common terminal of the pair of switching devices 13; the commonterminal of the pair of switching devices 13 is connected with the loadinductor 151; and, the load capacitor 152 of the load circuit 15 isconnected with the load inductor 151 through a terminal of the loadcapacitor 152. Therein, the first diode 121 and the second diode 122 areconnected with the top leg auxiliary switch 111, the bottom legauxiliary switch 112, the top leg switch 131 and the bottom leg switch132 through another terminal of the first diode 121 and another terminalof the second diode 122; and, the load capacitor 152 of the load circuit15 is connected with the top leg switch 131 and the bottom leg switch132 through another terminal of the load capacitor 152. Thus, a novelcircuit of reducing power loss of a switching device is obtained.

On using the present disclosure, whose switching power characteristicsare shown in FIG. 2, a gate-source voltage (Vs.) 3 is turned on to let acurrent flow through the pair of switching devices 13 when adrain-source voltage (Vs.) 2 of the pair of switching devices 13 isreduced to zero. Thus, switching loss of the pair of switching devices13 is reduced.

Please refer to FIG. 3A to FIG. 3F, which are views showing time seriescontrol modes of the circuit. As shown in the figures, each leg of acircuit has an additional switch and the modes of time series controlare shown. Significant modes include the modes shown in FIG. 3B and FIG.3C, where soft switching is formed by turning-on a top leg auxiliaryswitch 111 before turning-on a top leg switch 131 after electricity(Vs.) in parallel capacitor 133 of the top leg switch 131 is totallydischarged.

Please refer to FIG. 4 and FIG. 5, which is a view showing the state ofuse and a view showing time series control. As shown in the figures, apair of auxiliary switching devices 11, a pair of diodes 12, a pair ofswitching devices 13, a pair of auxiliary inductors 14 and a loadcircuit 15 are parallelly connected with another pair of auxiliaryswitching devices 11 a, another pair of diodes 12 a, another pair ofswitching devices 13 a, another pair of auxiliary inductors 14 a andanother load circuit 15 a.

Therein, control signals of MOSFETs are shown in FIG. 5, where top legauxiliary switches 111,111 a and bottom leg auxiliary switches 112,112 aof the auxiliary switching devices 11,11 a are turned-on earlier thantop leg switches 131,131 a and bottom leg switches 132,132 a of theswitching devices 13,13 a after a Vs. of a parallel capacitor of acorresponding MOSFET is totally discharged.

Thus, the present disclosure reduces power loss on switching where anadditional switch is used on each leg to reduce switching loss betweenturning on and off MOSFET.

To sum up, the present disclosure is a circuit of reducing power loss ofa switching device, where power loss happened between turning on and offMOSFET is reduced by applying an additional switch on each leg.

The preferred embodiment herein disclosed is not intended tounnecessarily limit the scope of the disclosure. Therefore, simplemodifications or variations belonging to the equivalent of the scope ofthe claims and the instructions disclosed herein for a patent are allwithin the scope of the present disclosure.

1. A circuit of reducing power loss of a switching device, comprising: apair of auxiliary switching devices, said pair of auxiliary switchingdevices being connected to a direct voltage, said pair of auxiliaryswitching devices comprising a top leg auxiliary switch and a bottom legauxiliary switch, said top leg auxiliary switch and said bottom legauxiliary switch being serially connected with each other, each of saidtop leg auxiliary switch and said bottom leg auxiliary switch being anauxiliary metal-oxide semiconductor field-effect transistor (MOSFET); apair of diodes, said pair of diodes being connected with said pair ofauxiliary switching devices, said diodes comprising a first diode and asecond diode; a pair of switching devices, said pair of diodescomprising a top leg switch and a bottom leg switch, said top leg switchand said bottom leg switch being serially connected with each other,said top leg switch and said bottom leg switch being switching MOSFETs,each of said top leg switch and said bottom leg switch being connectedwith a resonant capacitor parallelly; a pair of auxiliary inductors,said pair of auxiliary inductors being connected with said pair ofauxiliary switching devices and said pair of switching devices, saidpair of auxiliary inductors comprising a first inductor and a secondinductor, said first inductor and said second inductor being parallellyconnected with each other, each of said first inductor and said secondinductor having a first terminal and a second terminal; and a loadcircuit, said load circuit being connected with said pair of switchingdevices, said load circuit comprising a load inductor and a plurality ofload capacitors, wherein an auxiliary switching circuit comprising saidpair of auxiliary inductors, said pair of auxiliary switching devicesand said pair of diodes is obtained to fix each turn-on time of said topleg auxiliary switch and said bottom leg auxiliary switch, wherein, saidauxiliary switching device is turned on after a drain-source voltage ofa parallel capacitor of a corresponding MOSFET is totally discharged. 2.The circuit according to claim 1, wherein a common terminal of said pairof auxiliary switching devices is connected with said first terminal ofsaid second inductor.
 3. The circuit according to claim 1, wherein saidfirst diode and said second diode are connected with each other at apoint through a terminal of said first diode and a terminal of saidsecond diode, and wherein said first diode and said second diode areconnected to said first terminal of said first inductor at said point.4. The circuit according to claim 1, wherein said first diode and saidsecond diode are connected with said top leg auxiliary switch and saidbottom leg auxiliary switch through another terminal of said first diodeand another terminal of said second diode.
 5. The circuit according toclaim 1, wherein said first diode and said second diode are connectedwith said top leg switch and said bottom leg switch through anotherterminal of said first diode and another terminal of said second diode.6. The circuit according to claim 1, wherein a common terminal of saidpair of switching devices is connected with said load inductor.
 7. Thecircuit according to claim 1, wherein said second terminal of saidsecond inductor is connected with said second terminal of said firstinductor.
 8. The circuit according to claim 1, wherein said secondterminal of said second inductor is connected with a common terminal ofsaid pair of switching devices.
 9. The circuit according to claim 1,wherein an auxiliary transformer is obtained with said first inductorand said second inductor.
 10. The circuit according to claim 9, whereina ratio of a coil number of a secondary side of said auxiliarytransformer to a coil number of a primary side of said auxiliarytransformer is 1:n.
 11. The circuit according to claim 1, wherein saidload capacitor of said load circuit is connected with said load inductorthrough a terminal of said load capacitor.
 12. The circuit according toclaim 1, wherein said load capacitor of said load circuit is connectedwith said top leg switch and said bottom leg switch through anotherterminal of said load capacitor.